THIS Monday night will be, like, soooo ginormous because “Gossip Girl” is back – finally!

Blair, Serena, Chuck, Nate and the rest of the Upper East Side gang return with the first of five new episodes – and you can bet there’s trouble brewing among these privileged peers.

For starters, Blair (Leighton Meester) is back at school after her dalliance with bad-boy Chuck (Ed Westwick) – and not only has to confront tongues wagging about her slutty reputation but also has to adjust to losing her “Queen Bee” crown at Constance Billard School for Girls.

It won’t be easy.

Serena (Blake Lively), of course, will be there for her BFF Blair, but she’s preoccupied with her own problems – namely her new living arrangement with Chuck, who happens to be her future step-brother (their parents are marrying – oy!).

And if that’s not bad enough, we’ll learn Monday night that Serena is receiving “disturbing” packages from a stranger.

Things get even dicier in the second new “GG” episode, “Desperately Seeking Serena,” with the introduction of Georgina Sparks (Michelle Trachtenberg).

She arrives at Constance Billard armed with damaging info about her frenemy Serena – and her nastiness puts Blair to shame (can you imagine?).

“If you think Blair is the bitch of the show,” says a show insider, “this puts Georgina in perspective – Blair is afraid of her.”

And, if that’s not enough, one of the show’s major characters is about to be outed.